Dr. Vazquez's long-term goals are: 1) to become an independent physician-scientist who conducts high quality patient-oriented research that answers important clinical and epidemiologic questions 2) to become a role model and a mentor for younger physicians and 3) to become an expert in case-control and prospective cohort studies that integrate the tools of molecular biology in studies of viral infections in children. She plans to become an expert in these research methodologies using the studies as model systems that can then be successfully applied to other studies of pediatric infections. The proposed program of didactic training and intensive involvement in research, to which she will devote 80% of her time, will allow her to accomplish these goals. She has trained in Pediatric Infectious Diseases and has had successful experiences conducting patient-oriented research projects. She will spend up to 30% of her time in the first 3 years of the project period gaining advanced training in research methodology-in particular, advanced training in multivariable biostatistical methods and molecular biologic techniques and their application to her studies of pediatric infections, through graduate-level courses. With the guidance of her mentors, Dr. Shapiro &Dr. Kahn, she will conduct 2 studies: 1) A prospective longitudinal cohort study of human metapneumovirus (hMPV) infection in children. This study aims: a) to describe the clinical epidemiology of hMPV infection in children (including its association with wheezing and the development of asthma later in life);b) to identify risk factors for infection (eg, prematurity, exposure to cigarette smoke, race);and c) to define the molecular epidemiology of hMPV infection (e.g., the relationships among genotypes, associations between genotype and severity of illness, and differences in the strains from one epidemic year to the next) and 2) A matched case-control study of the long-term effectiveness of varicella vaccine in children that also aims to assess the effects of time since vaccination and of age at the time of vaccination on the effectiveness of the vaccine. Both studies target key public health issues and are likely to influence public health policy. The experience gained through the combination of didactic training and intensive research will provide the foundation for her to develop new studies of public health importance for which she will apply for independent R-01 funding by the end of the period of the proposed program.